The "robustness" is defined as a robustness of a behavior of a system against deviations. Since an actual system involves various kinds of deviations, a guarantee of the robustness is a very important issue in engineering. For example, when a behavior of a feedback loop system is not practically influenced by the introduction of a certain level of external disturbances thereinto, it is said that the system has a "robustness". As for the deviations, there are not only such external disturbances, but also internal variations of some parameter values caused by characteristic changes due to time passing of parts of the system.
The present inventor has already proposed a suiting method, in which a suiting region is previously set with respect to a physical characteristic, and functions (i.e. suiting functions) contained in the suiting region are found as a family of functions with parameters (cf. Unexamined Japanese Patent Publication (HEI) 7-226656)). According to the previous suiting method, a spread solution region is obtained, and, by using the spread solution region, a parameter design could be performed for a family of functions with a robustness against variations of parameter values.
In the parameter design according to a conventional method of optimizing method, for example, by minimizing a target function, only one optimized set of parameter values is obtained. Due to the obtained optimized parameter values being only one set without any spread, in the parameter design, it is impossible to take a quantitative robustness into consideration with respect to a change of a system behavior which is caused by the introduction of deviations of parameter values thereinto.
Also, in the aforementioned previous suiting method, in order to implement a suiting function, corresponding to the obtained parameter values, to a signal-processing device or the like, it is necessary to select only one set of parameter values from the solution region of the parameter values. Nevertheless, in the aforementioned previous suiting method, a general selection method for promoting a robustness of the suiting function is not especially prepared.
Further, in the aforementioned previous suiting method, there is a case where only one solution is calculated rather than a solution region. In order to obtain a solution uniquely, it is necessary to select how solution is calculated by using additional conditions because a solution of the suiting method ordinarily obtains a solution region. Nevertheless, in the past, the setting of uniformizing-conditions was not performed for promoting the robustness of the suiting function. Thus, generally, the obtained parameter values did not have the desired desired robustness.
Accordingly, in view of the above-mentioned problems, the present invention is directed to an improvement of the above-mentioned suiting method, such that solutions with robustness, and therefore robustly-stable physical systems, can be obtained when a solution region or a unique solution is needed.